This invention relates to manually-operated hydraulic linear actuators.
A linear actuator may be used for applying a force to a receiving member, such as a tool acting on a workpiece to move the workpiece relative to another member or to cut the workpiece or to compress the workpiece. For example, a linear actuator may be used in a rock trimmer to apply a force to a cutter for cleaving a rock sample into two or more pieces, each piece having a newly-produced face formed substantially along the cleaving line. Use of rock trimmers is generally preferred over saws and other mechanisms because trimmers produce faces that are substantially undamaged.
Although using rock trimmers is desirable, known forms of manually-operated rock trimmers have significant shortcomings. One form of rock trimmer employs a threaded member disposed through a frame, the frame being mounted on supports above a platform having a blade fitted thereon. The threaded member has a cutter at one end and a crank at the other end. By turning the crank in one direction, the threaded member is retracted in the frame away from the platform so that the trimmer can receive a rock sample on the blade. By turning the crank in the other direction, the threaded member is advanced downwardly toward the blade and platform so that the cutter engages the rock sample, the crank then being turned further to advance the cutter to cleave the sample into pieces.
This first form of rock trimmer has several important shortcomings, including that the mechanical advantage afforded by the crank is constrained by practical and operational limitations, particularly by the length of the crank and the pitch of the threads. For example, lengthening the crank to increase mechanical advantage can result in cumbersome and unstable operation, and also negate the compactness and impede the portability of the trimmer. Instability is particularly troublesome, and possibly hazardous to the operator and surrounding property. Instability arises due to the operator's application of force to the crank in a plane normal to the direction of cleaving and at a position above the rock sample, thereby introducing both tilting and rotational moments to the trimmer.
In turn, decreasing the pitch of the threads, while desirable to increase mechanical advantage, can result in unsuitably slow and mechanically-inefficient operation. Slow operation results because the number of turns of the crank necessary to retract and advance the member increases with decreasing pitch. Inefficient operation results because of friction between the threads and the frame. In particular, when the cutter is driven to cleave the rock sample, friction between the threads and frame increases. Friction requires the operator to do more work to cleave the sample than would be necessary in the absence of friction.
Another form of rock trimmer adds a hydraulic pump to the platform of the first trimmer. The pump holds the blade at the end of the pump piston, and is operated by a lever disposed under the rock sample, adjacent the platform. In this trimmer's operation, the crank is turned one way to retract the threaded member so that the trimmer can receive the rock sample on the blade and, then, the crank is turned the other way to advance the member so that the cutter and blade engage the sample. Once the sample is engaged, the hydraulic pump is actuated by pumping the lever, driving the blade upwardly toward the cutter to cleave the sample into pieces.
The second form of trimmer has several important shortcomings. For example, because the hydraulic pump is disposed below both the cutter and blade, debris produced from cleaving drops onto the extended pump piston. When the piston is later retracted, the debris can be drawn between the piston and its cylinder and possibly into the pump itself. In that event, the debris can degrade the pump's performance and can even cause pump failure, including by failure of the pump's seals.
The pump's disposition introduces other shortcomings, including several that are particularly troublesome when cleaving a relatively heavy, hard rock that protrudes beyond the dimensions of the trimmer. For example, operation of the pump's lever can be awkward due to its disposition below the rock and, therefore, can be difficult to reach and to pump. In addition, operation can also cause injury to the operator, including if one or more cleaved pieces of the rock fall from the elevated blade down onto the operator's pumping hand or if the operator strikes his hand on the rock during pumping, possibly repeatedly. Also, operation of this trimmer is manually inferior in that the pumping operation uses a lever that is isolated from the crank of the threaded member. That is, the operator is required to change hand positions between the lever and the crank in order to operate the trimmer. Moreover, the pumping action is applied to the trimmer at a location that not only reduces the operator's pumping leverage, but also impairs the operator's use of their pumping hand to counteract undesirable moments to which the trimmer can be subject. Furthermore, proper cleaving may be impeded due to reduced overall rigidity between the cutter and blade. Reduced rigidity arises because the cutter and blade both have free play and because cleaving force is not directed toward the platform and supporting structure; instead, cleaving force is directed from the blade disposed at the end of the extended pump piston upwardly away from the platform and through the cutter disposed at the end of the extended threaded member.
Accordingly, there is a need for an improved manually-operated rock trimmer that overcomes these and other limitations of conventional trimmers, particularly trimmers employing hydraulic mechanism.